To the Editor: Dr Schairer and colleagues1 conclude that the estrogen-progestin regimen is
associated with higher risks of breast cancer than estrogen alone. However,
several aspects of the study deserve careful consideration.

First, the study was not conducted in a representative sample of women
but in a select population for whom the risk of breast cancer may be high.
Only a sample of women who had neither surgery nor the recommendation for
it at baseline were included in the analysis. Furthermore, type of hormone
used was not assessed in the first phase of follow-up. Some hormone use was
measured retrospectively, possibly introducing recall bias.2
Moreover, the authors report no results for women who had mammography regularly.